A. Liquid Laundry Detergents in General
Detergents are substances used with water to remove soil from materials. Detergents are used under conditions which vary widely (e.g., type of soil, material to be cleaned, temperature and purity of water, desired physical form of detergent, etc.) and it is, therefore, not surprising that many different types of detergents are available. This invention concerns laundry detergents (sometimes called "heavy-duty" detergents) primarily formulated and used for cleaning clothes in washing machines.
All laundry detergents contain at least one surfactant. A surfactant is a substance whose molecules contain both hydrophilic and oleophilic groups. The surfactants are primarily responsible for the soil-removing properties of the laundry detergent, although other components of the detergent augment the surfactants. Surfactants are rountinely classified according to their electrostatic charge: the nonionics possess no electrostatic charge, the anionics possess a negative charge, the cationics possess a positive charge, and the amphoterics possess both positive and negative charges. When comparing the ability of a surfactant by itself to clean clothes, the nonionics generally outperform the other types of surfactants. The most common nonionic surfactants are the ethozylates, which include ethozylated alcohols, ethoxylated alkylphenols, and ethoxylated carboxylic esters.
Most laundry detergents also contain at least one builder. Builders aid the soil-removing properties of the surfactants in several ways. For example, builders help prevent the formation of insoluble soap deposits, aid in soap suspension, and help prevent the precipitation of certain calcium and magnesium salts. The most common builders are the phosphates, such as sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), tetrapotassium pyrophosphate (TKPP), and trisodium phosphate (TSP). However, the use of phosphates in detergents is banned in many parts of the U.S.A. for environmental reasons. Other types of builders include the citrates, the zeolites, the silicates and metasilicates, the polycarboxylate salts such as salts of nitrilotriacetic acid (NTA), the carbonates and bicarbonates, the phosphonates, the polymerics, and ethylenediaminetetracetic acid (EDTA) and its salts.
Laundry detergents are sold both as powders and as liquids. Although some powders are prepared by mixing together dry ingredients, the vast majority of powders are prepared by drying an aqueous slurry of ingredients (commonly known as a "crutcher mix"). Most powders contain anionic surfactants (which generally do not clean as well as the nonionics, but which are less expensive) and rather large amount of builders to improve their cleaning performance.
Liquid laundry detergents have been commercially available for many years and their popularity continues to increase, primarily because of their convenience to the customer. However, there continues to be difficulty in formulating a cost-competitive liquid laundry detergent which cleans as well as a powder. As mentioned above, most powders contain large amounts of builder to improve the cleaning performance of the surfactants. Unfortunately, many of the more effective builders have relatively low water solubilities. Furthermore, the solubility of builders decreases rapidly when most types of surfactants are added. For example, sodium carbonate is a relatively inexpensive builder and has a water solubility at 25.degree. C. of approximately 30 weight percent. However, its solubility drops to approximately 3 weight percent (a decrease of an order of magnitude) when only 1 percent of an ethoxylated alcohol nonionic surfactant is present. And even when the builders dissolve, there is a strong tendency for the water-surfactant-builder solution to later separate into two phases. Hydrotropes such as sodium xylene sulfonate or ethanol are sometimes used to improve solubility and to reduce phase separation, but the hydrotropes are relatively expensive and contribute little or nothing themselves to the cleaning performance of the laundry detergent.
In summary, most commercially available liquid laundry detergents contain very little or no builder and compensate by using larger amounts of surfactant and by using more effective (and more expensive) surfactants such as the ethoxylates. However, in spite of all the efforts directed at formulating liquid laundry detergents, it is still true that the liquids generally cost more and clean worse than the powders. Accordingly, there is a strong demand for a built liquid laundry detergent which: (1) is stable, homogeneous, and single-phase; (2) is cost-competitive with commercially available laundry liquids and powders; and (3) cleans as well as commercially available laundry liquids and powders.
B. Alkyl Glycosides in General
In addition to the ethoxylates, another type of nonionic surfactant which has been disclosed for use in liquid laundry detergents are the alkyl glycosides. A brief reveiw of alkyl glycoside chemistry is appropriate before considering their use in liquid laundry detergents.
Monosaccharides are polyhydroxy aldehydes and polyhydroxy ketones which, when unsubstituted, have the chemical formula C.sub.n H.sub.2n O.sub.n. Monosaccharides can join together, with the loss of water, to form chains of varying lengths. The length of a saccharide chain is commonly described either by added a descriptive prefix to its name or by stating the chain's "degree of polymerization" (abbreviated to "D.P."). For example, glucose (also known as dextrose) is a monosaccharide having a D.P. of one; sucrose and maltose are disaccharides having a D.P. of two; and starch and cellulose are polysaccharides having D.P.'s of 1000 or more. The term "saccharide" encompasses unsubstituted and substituted molecules of any chain length.
Glycosides are substituted saccharides in which the substituent group is attached, through an oxygen atom, to the aldehyde or ketone carbon. Accordingly, glycosides are considered acetals. As with the term "saccharide", the term "glycoside" defines neither the number nor the identity of the saccharide units in the molecule. To describe the number of saccharide units, the same methods are used as outlined above. To describe the identity of the saccharide units, it is common to modify the name of the saccharide unit by adding the ending "-side". For example, a glucoside is a glycoside having one or more glucose units and a fructoside is a glycoside having one or more fructose units.
A variety of substituent groups can be attached to the saccharide. However, for surfactant use, long-chain (i.e., 8 to 25 carbon atoms) alkyl substituent groups are most commonly employed because the resulting glycosides are highly surface-active due to the balancing of the hydrophilicity of their saccharide portions and the lipophilicity of their long-chain alkyl portions. It is also possible for oxy-alkylene groups to be attached between the saccharide and the long-chain alkyl group. For example, the compound having the following structure is a dodecyl (oxy-ethylene) glucoside of D.P.2: ##STR1##
The above compound can be represented by the following formula: EQU RO--(R'O).sub.x --Z.sub.y
where R is the dodecyl radical, R' is the ethylene radical, x is 1, Z is the glucose moiety, and y is 2.
C. Alkyl Glycosides as Surfactants and Solubilizers
A number of references have stated that alkyl glycosides are effective as surfactants in liquid laundry detergents and that alkyl glycosides exhibit solubilizing properties in certain applications. However, no known reference to date has appreciated or made use of the surprising (when compared to the ethoxylated nonionic surfactants) ability of alkyl glycosides to solubilize builders normally having low solubilities in aqueous surfactant solutions and no known reference to date has disclosed built liquid laundry detergents containing such high levels of these builders.
Ranauto, U.S. Pat. No. 3,721,633, issued Mar. 20, 1973, discloses liquid laundry detergent compositions containing alkyl glycosides and a builder selected from the group consisting of sodium nitrilotriacetate, potassium nitrilotriacetate, and potassium polyphosphate. These three builders are characterized by very high water solubilities (over 75 weight percent at 20.degree. C.). Ranauto states that these compositions exhibit stability against phase separation without the presence of a hydrotrope. The working examples in Ranauto show compositions comprising 25 to 40 weight percent builder, 10 to 20 weight percent surfactant, and 40 to 65 weight percent water.
Kaniecki, U.S. Pat. No. 4,147,652 issued Apr. 3, 1979, discloses aqueous alkali metal hydroxide cleaning compositions. Kaniecki states that the presence of alkyl glycoside surfactants helps solubilize the alkali metal hydroxide in concentrated solutions.
Payne, U.S. Pat. No. 4,396,520, issued Aug. 2, 1983, discloses a detergent powder composition comprising: (1) an alkyl glycoside surfactant; (2) a "calcium sensitive" anionic surfactant; and (3) from 0 to about 95 percent detergent builder. Suitable detergent builders are disclosed in Llenado, U.S. Pat. No. 4,303,556, issued Dec. 1, 1981, which Payne incorporates by reference. Payne states that the alkyl glycosides "not only provide excellent detergency themselves but [also solubilize] the calcium sensitive anionic detergent cosurfactant" so that "no special processing steps or processing aids are required" in preparing the crutcher mix.
Llenado, U.S. Pat. No. 4,483,779, issued Nov. 20, 1984, discloses a detergent composition comprising: (1) an alkyl glycoside surfactant; (2) a nonionic surfactant; (3) from 0 to about 90 percent detergent builder; and (4) an anionic optical brightener.
Jones, U.S. Pat. No. 4,483,787, issued Nov. 20, 1984, discloses laundry detergent compositions containing alkyl glycoside surfactants and alkylether sulfate surfactants. Jones states that the use of the alkyl glycoside "allows the preparation of more concentrated detergent compositions containing greater percentages of detergent surfactant which dissolve readily".
Urfer, U.S. Pat. No. 4,488,981, issued Dec. 18, 1984, discloses that lower alkyl glycosides reduce the viscosity of, and prevent phase separation in, aqueous liquid detergents.
Payne, U.S. Pat. No. 4,536,319, issued Aug. 20, 1985, discloses granular laundry detergents containing alkyl glycoside surfactants. Payne states that the alkyl glycoside surfactant "permits the formation of stable crutcher mixes with lower water content so the granules can be prepared very efficiently".